This invention relates to starting and operating apparatus for HID lamps and, more particularly, to such starting and operating apparatus which operate HID lamps at high frequency and with high power factor and which also provide standby incandescent lighting.
Miniature high-pressure metal-vapor discharge lamps are described in U.S. Pat. No. 4,161,672, dated July 19, 1979 to Cap et al. Such lamps are known to have potential utility as screw-in replacements for incandescent lamps. These lamps operate efficiently at predetermined high frequencies as disclosed in U.S. Pat. No. 4,170,746, dated Oct. 9, 1979 to Davenport. In the usual case, with DC or high-frequency operation, it is normally required that the available AC be rectified and filtered which substantially reduces the power factor of the operating system. This is undesirable and in many European markets, for example, high power factor operation is a requirement.
It is known to operate discharge lamps with a rectified current wherein a current-limiting impedance is included in the line prior to rectification and such a mode of operation is shown in U.S. Pat. No. 3,787,751, dated Jan. 22, 1974 to Farrow. A variety of such arrangements are also shown in U.S. Pat. No. 4,084,217, dated Apr. 11, 1978 to Bradli et al and U.S. Pat. No. 4,187,449, dated Feb. 5, 1982 to Knoble. Another system is described in the referenced copending application Ser. No. 347,274, filed Feb. 11, 1982 by J. M. Hicks et al.
When HID lamps are first started, they normally require a short time up to a few minutes, depending on the lamp design, to warm up and generate operating pressure within the envelope in order to produce full light output. In addition, after momentary periods of power interruption, the lamps normally must cool down at least to a warm condition before they can be reignited, after which the pressure must build up again to achieve rated light output. It is known to provide standby incandescent lighting for such lamps and a wide variety of circuits are available. One such standby lighting system is disclosed in U.S. Pat. No. 3,517,254, dated June 23, 1970 to McNamara. Another type of standby lighting system is disclosed in U.S. Pat. No. 3,723,808, dated Mar. 27, 1973 to Jones. U.S. Pat. No. 4,170,744, dated Oct. 9, 1979 to Hansler discloses a standby lighting system for use with a miniature metal-vapor lamp, with the combination formed as a screw-in light source.